Scientists say they've found more evidence that so-called early-birds and late risers are that way because of their genes. Researchers say the finding helps them better understand how our internal clock operates, and it has implications for treating sleep disorders.

As the saying goes, early to bed, early to rise. But in the world of sleep researchers, that's a disorder as much as the syndrome experienced by people who stay up very late and sleep very late into the morning.

Humans operate on a 24-hour clock. This involuntary, internal mechanism, known as a circadian rhythm, determines how long we sleep and when.

Researchers, including neurologist Louis Ptacek of the Howard Hughes Medical Institute, discovered a defect in a gene known as Per2 that helps regulate the circadian rhythm.

This week in the journal Nature, Dr. Ptacek and colleagues at Howard Hughes Institute at the University of California in San Francisco report the discovery of another mutated gene in a completely different family, known as CK1delta. "If you think of it simply as gears as in a clock. And the clock is ticking too fast, it could be a problem in one gear or as it is in Per2, in one large family, it could be a mutation in a different gear, in this case, CK1delta," he said.

The researchers discovered the defective gene in a family of early risers.

When the gene was put into mice, the rodents exhibited early bird behavior. When the same gene was introduced into fruit flies, however, it shifted their circadian rhythm and turned them into larks.

Dr. Ptacek says using the same gene to study behavior among different species might lead to the discovery of other molecular mechanisms involved in human sleep disorders.

He estimates three out of 10 people have some form of sleep disorder. He says gene discoveries of what makes our internal clocks tick could lead to a treatment for a sleep disorder that's common among the elderly. "As we age, we all have a tendency to fall asleep earlier and rise earlier. And in some cases, that's problematic for older people who wake up when it's cold, dark and lonely. So, that common finding that we think is a part of normal human aging is yet another very common example of where a medicine that helps us adjust our clocks might lead to a better quality of life for people," he said.

Researchers say all six family members in the study with the early bird gene also suffer from asthma, depression and migraine headaches. Scientists believe there may be a connection between those diseases and sleep disorders.

Physiologist Tom Feroah of the Medical College of Wisconsin in Milwaukee has observed nearly identical rats, and concluded that multiple genetic differences are responsible for different sleep patterns.

Professor Feroah says it's not surprising that people with sleep disorders appear to suffer from diseases. He says the circadian rhythm regulates the body through miniature slave clocks in each cell, which in turn integrates the immune system, temperature regulation, hormones and all brain functions.

"So we have this wonderful overall integration of all the physiology, in which when we try to not sleep properly, be trained to the television or light and not to the daily light and dark cycle or have bad sleep habits, that we tend to uncouple the whole body function. It tends to go in different directions at different times of the day, that we tend to feel more stress, not be able release stress as well, not sleep well, not heal as well, have higher tendency for disease," he said.

People who sleep poorly and are unable to get enough deep sleep at the beginning of the rest cycle, have more heart disease, high blood pressure and stroke, conditions that researchers now believe are caused by a malfunctioning immune system.

Researchers hope to discover more sleep genes. Laboratory studies so far show that a small alteration in the newly discovered CK1delta gene quiets the activity of a protein that seems to disrupt sleep, which might be good news for people who can't get a good night's rest.